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Review: Define your terms

18 April 1992

By ANTONY ANDERSON

Artificial Intelligence from A to Z by Jenny Raggett and William Bains,
Chapman and Hall, pp 256, £11.95 pbk

The familiar meaning of the word abduction derives from its legal definition:
‘The unlawful carrying off of a person by force especially a young woman
or ward.’ The picture that springs to mind is of a villain carrying off
a heroine to steal her money. Abduction is a good example of a word that
may cause confusion when used in other contexts. For example, it has quite
different and less melodramatic connotations when used as a non-legal technical
term: in physiology, for example, for the muscular action of moving a limb
away from the body; or in logic where it is used to define a particular
kind of syllogism in which the minor premise and therefore the conclusion
is merely probable. In the specialised field of artificial intelligence
it has come to mean the kind of reasoning that explains effects in terms
of causes. This contrasts with deduction, which reasons particular consequences
from general principles.

Abduction is the opening definition in Artificial Intelligence from
A to Z, a glossary designed for anyone who wants clear, short and non-technical
explanations of about 200 terms used in artificial intelligence and related
computer technologies. It isn’t intended for the academic but for ‘librarians,
lawyers, journalists, consultants, linguists, doctors and a hundred and
one other professionals who want to know what a word means without too much
fuss’.

It is timely, because many of the ideas and techniques developed in
artificial intelligence research are creeping into commercial computer applications.
For example, computer programmers brought up on sequential computer programming
languages like Fortran or Cobol are having to adapt to logic programming,
a method whereby knowledge is represented and used according to certain
laws of mathematical logic, and to object-oriented programming, in which
fragments of computer code encapsulate everything to do with each idea used
by the computer program.

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The book covers a wide field: chaos and certainty; knowledge engineering
and expert systems; metaknowledge, or the knowledge about knowledge; object
oriented programming; parallel processing and neural networks. The language
is clear, the examples and illustrations are often amusing and memorable.
For example, a list is a data structure used in many AI languages like LISP.
The processing of a list is explained by the classic puzzle of the cannibals
and missionaries in which two cannibals and two missionaries have to cross
a river in a boat that only holds two people. Only missionaries can row
and, if cannibals outnumber missionaries on either bank, then they eat the
missionaries. What sequence of transfers is required? The problem is usually
solved with much moving of matches on the table, but a list processing language
can handle problems of this kind well. Combinational explosion, or the way
in which the complexity of problems seems to explode as the problems get
bigger, is explained with selecting five Russian dolls out of a box at random
to find a set that nest inside one another correctly. As more dolls are
added to the box, the number of possible sets of dolls shoots up as does
the time taken to select the matching set.

I have always thought paradigm was an overused word that needed putting
in its place, but have never dared to say so. Why is it so popular when
it trips ill off the tongue and kills discussion?

Raggett and Bains suggest that paradigm – pattern or model – should
be used in moderation and not as a synonym, for example, for a theory, idea
or hypothesis, way of looking at things or my latest product. I don’t suppose
for a moment that from now on paradigm will get its marching orders and
be banished to footnote or appendix. Nevertheless, those readers of New
Scientist who get a sinking feeling when they hear the word, or have a recurrent
nightmare in which they read the headline: ‘Top Fashion Paradigm to Wed’
will find this book a model of clear exposition.

This glossary is not exhaustive: there is no definition of artificial
intelligence, which is odd – considering the title or of inheritance, which
is surprising, considering its importance in many AI systems. Nevertheless
I thoroughly recommend the book. If you have difficultly in remembering
what the difference is between forward and backward chaining, then this
is the book for you.